1. Field of the Invention
The present invention relates generally to shaped three-dimensional nanoscale-to-microscale structures, and more specifically to methods of producing shaped nanoscale-to-microscale structures from nanoscale-to-microscale templates having an original chemical composition and an original shape, and subjecting the nanoscale-to-microscale templates to a chemical reaction, so as to partially or completely convert the nanoscale-to-microscale template into the shaped nanoscale-to-microscale structure having a chemical composition different than the original chemical composition and having substantially the same shape as the original shape, being a scaled version of the original shape.
2. Description of Related Art
Intensive global research and development activity is underway to develop methods for assembling nanoscale-to-microscale devices with complex shapes and fine features for a host of biomedical, telecommunications, computing, environmental, aerospace, automotive, manufacturing, energy production, chemical/petrochemical, defense, and numerous other applications. Microscale devices have already found use as sensors in automotive and some medical applications. However, a far larger untapped potential exists for the use of new three-dimensional nanoscale-to-microscale devices in a variety of advanced applications, such as in:
i) medicine (e.g., targeted drug or radiation delivery; rapid clinical and genomic analyses; in vitro sensors; micro/nanoscale surgical tools, pumps, valves, and components used in biomedical imaging, etc.),
ii) transportation and energy production (e.g., new sensors and actuators for enhanced engine performance and energy utilization; micro/nanoscale components for automotive, diesel, jet, or rocket engines; micro/nanoscale components for turbines used in energy conversion or generation; micro/nanoscale reactors, pumps, bearings, etc.),
iii) communications and computing (e.g., micro/nanoscale optical devices, actuators, switches, transducers, etc.),
iv) environmental remediation (e.g., active micro/nanostructured filter or membrane materials for the scrubbing of gas exhausts for pollutant gases or particles or for the treatment of wastewater streams),
v) agriculture (e.g., micro/nanoscale carriers for fertilizers or for delivering nutrients to animals), and
vi) production/manufacturing of food, chemical, and materials (e.g., micro/nanoscale on-line sensors, reactors, pumps, dies, etc.), and a variety of consumer products (e.g., for lighting, portable electrical devices, water purification, etc.).
The widespread commercial application of three-dimensional nanostructured micro-assemblies requires processing protocols that can be scaled up for mass production on a large (up to tonnage) scale, while precisely preserving morphological features on a small (down to nanometer) scale. Developing processing protocols that satisfy both of these often-conflicting requirements of scalability and precision remains a significant challenge.
Elegant examples of large scale fabrication of three-dimensional microstructures with nanoscale features can be found in nature. Certain microorganisms are adept at assembling biomineralized structures with precise shapes and fine (sub-micron) features. For example, diatoms are single-celled algae that generate an exceptional variety of intricate microshells based on silicon dioxide. Each diatom microshell (a frustule) possesses a three-dimensional shape decorated with a regular pattern of fine features (102 nm pores, channels, protuberances, ridges, etc.) that are species specific; that is, the frustule shapes and fine features are under genetic control.
The frustule morphology for a given diatom species is replicated with high fidelity upon biological reproduction. Consequently, enormous numbers of identically-shaped frustules can be generated by sustained reproduction of a single parent diatom (e.g., more than 1 trillion daughter diatoms with similar frustules could be produced from a parent diatom after only 40 reproduction cycles). Such massively parallel and genetically precise three-dimensional nanoparticle assembly has no man-made analog. With tens of thousands of extant diatom species, a rich variety of frustule morphologies exists for potential device applications.
This range of diatom frustule morphologies may be further enhanced through genetic modification of diatoms. The recent mapping of the genome of the diatom Thalassiosira pseudonana is a first step in this direction. A number of other organisms (e.g., silicoflagellates, radiolarians, sponges, various plants, mollusks) also form controlled silica-based microstructures. Biomineralized calcium carbonate-based structures are also formed by a variety of organisms (e.g., algae, mollusks, arthropods, echinoderms, bacteria, plants). For example, coccolithophorids are micro-algae that form a rich variety of intricate three-dimensional calcium carbonate-based microshells.
While a wide variety of shapes and fine features can be found among the various biomineralized structures, the natural chemistries of such structures are largely based on calcium compounds (carbonates, phosphates, oxalates, halides) or silica. Such limited chemistries severely restrict the properties (e.g., electronic, biomedical, chemical/catalytic, optical, thermal) of such micro/nanostructures for device applications. If such micro/nanostructures could be converted into a much wider range of chemistries, without a loss of the biologically-derived shapes or fine features, then the massively parallel and genetically precise three-dimensional self-assembly characteristics of nature could be synergistically coupled with such chemical tailoring to enable the mass production of enormous numbers of nanoscale-to-microscale devices with a diverse range of properties for numerous applications.
Recent work has shown how gas/solid displacement reactions of the following type may be used to convert silica diatom microshells into non-silica-based compositions without a loss of the starting microshell shapes and fine features:2Mg(g)+SiO2(s)=>2MgO(s)+{Si}  (1)
where {Si} refers to a Si-bearing product. The shapes and fine features of the starting diatom microshells were well preserved in the MgO-based microshell replicas. Other oxidation-reduction reactions may be used to generate a wide variety of oxide/metal composite replicas.
For example, U.S. Pat. No. 7,067,1041 discloses beneficial methods of producing shaped microcomponents from biologically-derived silica microtemplates, namely diatom microshells, wherein the microshells are converted into microtemplates comprising solid oxides.
Yet, it would be more beneficial to provide a more general fabrication method not so limited to biological microtemplates/diatom silica microshells.
It further would be beneficial to provide production methods for microcomponents that are not limited to comprising of oxides, such that nanoscale-to-microscale devices can be fabricated that are formed of elements, alloys of elements, or non-oxides such as carbides.
Work to date has not demonstrated, however, how nanostructured micro-assemblies (such as diatom microshells) may be reactively converted into inorganic replicas comprised solely of an element (such as silicon), a metallic alloy (such as a silicon alloy), or a non-oxide compound (such as silicon carbide or silicon nitride). Nanocrystalline silicon-based devices, for example, can exhibit attractive electronic or optical properties (e.g., photoluminescence). Nanocrystalline silicon carbide-based devices and silicon nitride-based devices can exhibit attractive electronic, chemical, and mechanical properties (e.g., high strength).
Thus, it is a provision of the present invention to provide a more general fabrication process than that conventionally known, including the ability to fabricate nanoscale-to-microscale devices beyond those fabricated only from biological microtemplates/diatom silica microshells, and where such devices are formed from the syntheses of non-oxide bearing products. It is to such a method that the present invention is primarily directed.